Advances in Knee Replacement Surgery
Dr B.R.Prashanth
MS, MCh, MRCS Ed, MRCS Eng, FACSM
Joint Replacement Surgeon
Mysore
Total knee replacement or commonly called as TKR is one of the most
successful and life-enhancing surgical procedures. It relieves almost all pain
for most patients who have the procedure, allowing them to return to work and
tremendously enhancing their quality of life. TKR is performed for severe
degenerative disease of the knee joint.
The goal of knee replacement is to provide a pain-free knee that allows
relatively normal activities and lasts for a long time. To achieve these goals, it
is important that the knee implants be inserted with proper positioning. The
bones and ligaments are prepared very carefully to allow the knee to be
functional and durable.
The Right Implant for You
The brand and design used by your Joint Replacement Surgeon depends on
many factors, including your needs (based on your age, weight, activity level,
and health), your doctor's experience and familiarity with the device, and the
cost and performance record of the implant.
Implant Components
Knee implant components
Dr Prashanth and team performing a Bilateral Knee replacement
Up to three bone surfaces are replaced in a Total knee Replacement:
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The lower ends of the femur. The metal femoral component curves
around the end of the femur (thighbone). It is grooved so the kneecap
can move up and down smoothly against the bone as the knee bends
and straightens.
The top surface of the tibia. The tibial component is typically a flat
metal platform with a cushion of strong, durable plastic, called
polyethylene. For additional stability, the metal portion of the
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component may have a stem that inserts into the center of the tibia
bone.
The back surface of the patella (Knee cap). The patellar component
is a dome-shaped piece of polyethylene that duplicates the shape of
the patella.
Types of Prosthesis
Fixed-Bearing Prosthesis
Most patients get a fixed-bearing prosthesis. In this design, the polyethylene
of the tibial component is attached firmly to the metal implant beneath. The
femoral component then rolls on this cushioned surface.
Mobile-Bearing Prosthesis
If you are younger, more active, and or overweight, your Surgeon may
recommend a rotating platform /mobile-bearing knee replacement. These
implants are designed for potentially longer performance with less wear.
Like fixed-bearing implants, mobile-bearing implants use three components to
provide a relatively natural joint. In a mobile-bearing knee, however, the
polyethylene insert can rotate short distances inside the metal tibial tray.
This is designed to allow patients a few degrees of greater rotation to the
medial and lateral sides of their knee.
Compared with fixed-bearing designs, mobile-bearing knee implants require
more support from soft tissues, such as the ligaments surrounding the knee.
They also cost more than fixed-bearing implants.
Implant Materials
The metal parts of the implant are made of titanium and or cobalt-chromium
based alloys or the latest Oxinium implant. The plastic parts are made of
ultrahigh molecular weight polyethylene. All together, the components weigh
between 15 and 20 ounces, depending on the size selected.
What Are Recent Advances in Knee Replacement Surgery?
Minimally invasive TKR
Minimally invasive surgery has revolutionized knee replacement surgery as
well as many fields of medicine. Its key characteristic is that it uses
specialized techniques and instruments to enable the surgeon to perform
major surgery without a large incision. Minimally invasive total knee
replacement involves the use of a smaller incision than the one used in
traditional knee replacement. In the traditional method, the incision averages
8 to 10 inches in length. In Minimally invasive knee surgery, the incision is
only 4 to 6 inches long. Because there is less damage to the tissue around
the knee, patients who undergo this procedure expects a shorter hospital
stay, a shorter recovery, and a better looking scar.
Currently this less invasive procedure is performed by only a small
percentage of Orthopaedic surgeons in India as it needs expertise.
Oxinium Knee implant
OXINIUM, Oxidized Zirconium is a metal alloy consisting of 97.5% zirconium
and 2.5% niobium, two of the most biocompatible metals known to man.
Oxinium is a superior implant that is expected to last longer and will
allow active, younger patients to benefit much earlier from a replacement
knee. With this material’s resistance to abrasion and anticipated longevity,
patients can once again enjoy an active lifestyle for nearly thirty years with
oxinium implants when compared to the regularly used Cobalt chromium
implant. Significant advantages include the durability, improved wear
resistance and biocompatibility especially for patients who have metal
allergies and is expensive compared to the other implants.
Gender specific Implants
Recent developments in design include "gender specific" implants. A number
of studies indicate that the shape and proportions of a woman's knee differ
from those of a man's knee. As a result, several manufacturers have
developed components which more closely match the average woman's knee.
However, there are no studies to show that "gender specific" implants last
longer or provide better function than standard implants.
Patient specific blocks and Implants
More recently, several new technologies have been introduced. The first are
patient-specific cutting blocks. With this technology, the patient receives either
a CT scan or an MRI. The scan is then sent to the manufacturing company.
Technicians measure certain anatomical features of the patient's knee. A
computerized surgical plan is sent to the surgeon. This plan contains detailed
information as to the appropriate size implants and location of the bone cuts.
After approval by the surgeon, the manufacturer creates specialized cutting
blocks for that particular patient. These cutting blocks allow for bone cuts to
be made with the patient's specific anatomy in mind to allow for optimal fit and
alignment. Patient specific implants have also emerged, which, theoretically,
may lead to longer implant life, more range of motion, and a quicker
operation. However, "off-the-shelf" implants are still utilized.
Computer-Assisted Knee Replacement Surgery (CAS)
Computer-assisted knee replacement surgery allows surgeons to operate with
smaller incisions and greater precision:
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Surgeons can align a patient's bones and knee replacement implants
with a degree of accuracy not possible with the naked eye
Smaller incisions with CAS offer the potential for faster recovery, less
bleeding, and less pain for patients
Computers used during orthopaedic surgery offer visual mapping to help
Surgeons make crucial decisions before and throughout the knee
replacement operation. The key is to combine the precision and accuracy of
computer technology with the surgeon's skill to perform surgery.
Cementless Implants
Cementless fixation relies on new bone growing into the surface of the implant
for fixation. Cementless implants are made of a material that attracts new
bone growth. Most are textured or coated so that the new bone actually grows
into the surface of the implant and is expensive.
Your Joint Replacement surgeon will evaluate your situation carefully before
making any decisions about components and fixation and the type of implant
that best meets your needs. Finally, a total knee Replacement relieves pain
and helps you live a fuller and more active life. The above advancements are
now being performed at Columbiaasia Hospital says Dr B.R.Prashanth, Joint
Replacement Surgeon Hospital, Mysore. Further information from
9845511760 or 0821 – 4288217, E mail: orthoprash@yahoo.co.uk.